Metathesis reaction is used for the conversion of olefins. In the metathesis reaction, olefins of the same or different kinds are reacted with each other to yield olefins having different structures, for example, metathesis of ethylene and butene to propylene and metathesis of butene to pentene and propylene.
Various catalysts have been developed for olefins metathesis. Among these, catalysts having an oxide of molybdenum, tungsten and rhenium supported on a high surface area carrier receive highest industrial interest.
Molybdenum- and tungsten-based catalysts are more widely used in industrial metathesis processes due to their higher tolerance to catalyst poisonous substances and less expensive cost. However, they are known to be less active comparing to rhenium and therefore require higher temperature, typically above 100° C., and preferably above 200° C., in order to achieve a desired activity. The higher temperature employed conveniently results in reduced selectivity due to occurrence of side reactions, such as olefin isomerization and oligomerization.
Rhenium is highly active in olefins metathesis. It can be operated in a significantly lower temperature range. However, its rapid deactivation is a major drawback.
European patent application EP 027817 A1 discloses an olefin metathesis process carrying out in the presence of a rhenium catalyst in a moving bed reaction zone wherein the catalyst is then reoxidized in a connected regeneration zone. This enables the process to be continuously operated despite the high deactivation rate of the rhenium catalyst. However, a moving bed process is much more complex and energy consuming, and therefore is normally less desirable in industrial applications, especially comparing to a fixed bed system.
U.S. Pat. No. 6,277,781 B1 discloses a method for reducing deactivation rate of a rhenium-based metathesis catalyst, the method comprising treating the catalyst at a temperature of more than 750° C. in a hydrocarbon-containing stream, e.g. a methane stream, in the presence of hydrogen, and activating under a non-reduction atmosphere at a temperature in the range of 400-1,000° C. prior to carrying out metathesis reaction and it is preferred that the catalyst contains some amount of cesium.
Therefore, it is an object of the present invention to provide a stabilized rhenium-based heterogeneous catalyst overcoming the drawbacks of the prior art, in particular displaying improved reaction stability and tolerance to poisonous substances.
It is a further object of the present invention to provide a stabilized rhenium-based heterogeneous catalyst which allows use of the catalyst in a fixed bed reactor.
Also another object of the present invention is to provide an improved process for production of an olefin compound in which the operating cycle time is increased.